Of the Box

Plants Can Hear When They’re Being Eaten — and They Fight Back

What’s the difference between plants and animals? If your answer is that animals are intelligent and plants aren’t, you’ve got another thing coming. Evidence is mounting that plants are way more complex than scientists previously realized. Here’s just one more example of their intelligence: some plants can hear when they’re being eaten, and they defend themselves in response.

Bad Vibes
Scientists have known that sound waves can have an effect on things like germination and growth, but University of Missouri researchers Rex Cocroft and Heidi Appel wanted to figure out whether plants could also sense the vibrations that insects produced when munching on them.

Using a vibration microphone equipped with laser sensors, Cocroft recorded the sounds of caterpillars chowing down on the delicious leaves of Arabidopsis thaliana, a small flowering plant related to cabbage and mustard. They chose that plant for the fact that it produces mustard oil in its leaves. “A caterpillar that eats nothing but mustard oil plants can get poisoned if the levels get too high,” Appel told Farm Journal.

When they played the sounds of caterpillar chomps for Arabidopsis, the plants sent out extra mustard oils into their leaves. Not so with other sounds like wind or insect song (which, to a plant, we assume sounds like a velociraptor). “This indicates that the plants are able to distinguish feeding vibrations from other common sources of environmental vibration,” Cocroft said in a press release. The plants that heard the vicious caterpillar attack also produced more anthocyanins, the chemical that gives flowers their red color.

What This Means
Of course, those extra mustard oils take anywhere from a few hours to several days to build up. Appel compared the response to cocking a gun: the vibrations warn the plant that more attacks could be coming, so it gears up for war.

“This research also opens the window of plant behavior a little wider, showing that plants have many of the same responses to outside influences that animals do, even though the responses look different,” he said. And why wouldn’t they? Plants have to eat, breathe, reproduce, and defend against predators just like their animal brethren. To assume they wouldn’t have sophisticated ways to do those things would be selling them short.

And if you think that’s hard core, just wait until you see what tomato plants do when caterpillars come to dine. It’s incredibly metal.